Casein is the predominant phosphoprotein, that accounts for nearly 80% of proteins in cow milk and cheese. Milk-clotting proteases act on the soluble portion of the caseins. K Casein, thus originating an unstable micellar state that results in clot formation. When coagulated with chymosin, casein is sometimes called paracasein.
Casein is not coagulated by heat. It is precipitated by acids and by rennet enzymes, a proteolytic enzyme typically obtained from the stomachs of calves.